The smooth pursuit responses to 5 degrees and 20 degrees/sec constant-velocity stimuli were recorded from 23 patients with schizophrenia, 16 affective disorder patients, and 21 normals using low-noise infrared oculography. Pursuit gain, catch-up saccade (CUS) rate and amplitude, and their interrelationships were examined. Gain in the schizophrenic patients was reduced only at 20 degrees/sec, but for both patient groups, CUS rate at 5 degrees/sec was significantly lower than in normals. Using CUS rate at 20 degrees/sec, the patient groups could be distinguished from each other (the rate for schizophrenic patients being highest, and the rate for affectives the lowest) but neither differed significantly from normals. The diagnostic groups did not differ significantly in mean CUS amplitude, although there was a trend for patients to have larger saccades. Gain-CUS rate correlation was strong in normals but reduced or absent in both patient groups. These results indicate that the ocular motor systems of patients with schizophrenia and affective disorders process eye position error abnormally.